What's the problem with my NDS Lite touch panel?

hi guys:
I got a NDS Lite touch panel from e-bay and try pretty much all of the example from the internet. However, it wouldn't work for some reason. The Serial Monitor may correctly display the X-axis value (the value change by position you press on the touch panel), but the Y-Axis is either 0 or some other value. Is any one who knows what's going on with this issue?